1. Field of the Invention
The present invention relates to a writable optical data recording medium comprising a data recording layer composed of a dye material, and a manufacturing method therefor.
2. Description of the Related Art
A writable optical data recording medium which has a data recording layer composed of a water-insoluble organic dye material and which produces an output signal conforming to the CD format in reproduction of its recorded data has been known. This type of recording medium is called as WO(write once) type CD (Compact Disk) and is disclosed in, for example, Japanese Laid-Open No.2-289,935 and U.S. Pat. No. 5,021,276. This WO type CD has a structure in which a data recording layer composed of a dye material, a metal reflective layer, and a protective layer of a UV curing type resin are successively formed on a surface having a pre-formatted pattern of a transparent substrate. In recording, a laser beam is irradiated through the transparent substrate to the recording layer to heat the dye material by virtue of the absorption of the laser light. The heat decomposes the dye material to change the optical property of the data recording layer, and causes deformation of the transparent substrate placed under the data recording layer. When the recorded data is reproduced, a low-powered laser beam, unaffecting the data recording layer, is irradiated to the recorded area along the tracks, and then a difference between intensities of the reflected lights from the recorded portion and unrecorded portion is detected.
In accordance with the CD Standard, the WO type CD has to have 65% or more reflectivity with a laser beam for reproduction to be able to reproduce the data by an available CD players. In order to satisfy such a standard, the above-mentioned WO type CD uses gold metal for the metal reflective layer material. However, it goes without saying that the use of gold or silver metal as a reflective layer material increases the manufacturing cost of the WO type CD and its price accordingly.
In order to reduce the cost for manufacturing the WO type CDs, a WO type CD using aluminum for its metal reflective layer material has been proposed, for example, as described in Television Journal Vol.48(1994), No.5, pp 584-590.
The WO type CD using aluminum for its metal reflective layer material intends to seemingly heighten the reflectivity of the WO type CD by forming a light interference layer on the incident side of a recording or reproduction beam to cause multi-interference of the incident light. Accordingly, the WO type CD has a light interference layer as an essential part. However, since the light interference layer is formed by a process of sputtering an inorganic dielectric material, the process increases the total cost for manufacturing the WO type CD.